Expression of Early Genes in Estrogen Induced Phenotypic Conversion of Neuroblastoma Cells

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Abstract
Estrogens are known to modulate the growth rate and differentiation state of a number of cells. In uterine, as well as in mammary tumor cells, estrogen‐dependent proliferation and differentiation are correlated to a series of biochemical responses, including increased expression of proto‐oncogenes such as:, c‐fos, c‐jun and c‐myc. Since estrogens were shown to regulate the proliferation and the differentiation state of cells of nervous origin, the aim of the present study was to investigate whether these effects were associated to changes in the expression of early genes. In the model system utilized, the human cell line SK‐ER3, an increase in c‐fos mRNA and Fos protein without change of c‐jun and related genes mRNA concentration was observed after short term treatment with 17β‐estradiol (E2). A significant decrease of c‐fos, c‐jun and jun‐D proto‐oncogene mRNA levels were found after prolonged hormonal treatment. The exposure to the hormone did not determine any change in N‐myc expression. Since the three protooncogene mRNAs are rapidly induced following estrogen treatment in other cell systems and target tissues, it is concluded that the estrogen‐induced differentiation of neuroblastoma cells is correlated to a pattern of expression of early genes that might be peculiar for the activity of this hormone in neural cells.